1. Field of the Invention
The present invention relates to mass spectrometry and a mass spectroscope.
2. Description of the Prior Arts
In recent years, a mass spectroscope has been often used for analysis of a sample. A mass spectroscope is used in a manner that a sample is ionized, and the mass is selected by scanning an electric field or a magnetic field thereby to detect ions that are selected by scanning. An output (mass spectrum) is thus obtained for the mass. The sample is ionized by imparting electric charge to the sample, such as by causing electrons to impinge onto the sample (EI method), spraying the sample under a high voltage (electrospray method/ESI method) or chemically ionizing the sample (atmospheric-pressure chemical ionization method/APCI method). Such technologies have been disclosed in, for example, Japanese Patent Laid-Open No. 9359/1989.
As described above, when electric charge is imparted to electrons, electron impingement, high voltage or large chemical energy are involved. Therefore, impurities are inevitably produced. By the EI method, for example, the sample is destroyed by the bombardment with electrons and, hence, ions having masses different from that of the sample to be measured are produced in large amounts. Such impurities are mixed into the sample to be measured and cause the measurement precision to lower. In particular, when impurities adhere to the interior of the mass spectroscope and are accumulated to contaminate the interior of the mass spectroscope, the measurement precision is greatly deteriorated and the results of analysis become no longer reliable.
The object of the present invention is to provide a mass spectrometry and a mass spectroscope capable of verifying the reliability of the results of analysis.
In order to accomplish the above-mentioned object according to the present invention, the sample is ionized, the ionized sample is separated depending upon the mass, the quantity corresponding to a specific mass number included in the sample as a result of separation is measured, common detection items of the separated sample and a different sample are compared, or different detected quantities in the same sample are compared, and the data on reliability are output based upon the comparison.
Preferably, the mass spectrum of a reference sample is stored at the time of measuring the reference sample, and the mass spectrum of the reference sample that is stored is compared with the mass spectrum of an unknown sample at the time of measuring the unknown sample, in order to judge the reliability of whether the quantitative object component is correctly measured or not.
In a general mass spectroscope, furthermore, it is preferable that the mass spectra having close densities are compared with each other though the pattern of mass spectrum varies depending upon the concentration of a sample due to chemical ionization reaction among sample molecules. This makes it possible to minimize the influence due to a change in the pattern of the mass spectrum caused by a change in the concentration and, hence, to improve the reliability of the results of determination. In particular, it is necessary to calculate the concentration of an unknown sample from a calibration curve, and to compare a reference sample having a concentration closest to the concentration of the known sample with the unknown sample. Whether the object component is quantitatively determined correctly or not is judged by comparing numerical values of the degrees of similarity of the mass spectrum of the reference sample to the mass spectrum of the unknown sample, the difference in the evaluation of reliability of the results of quantitative determination that varies depending upon the degree of skill of the person who conducts the analysis. When the concentration of the sample lowers, the reliability of the degree of analogy is degraded by the influence of peaks such as the background peak, and the adjacent peaks, and by random noise. However, the reliability of the degree of analogy is improved by purification by automatically removing the background peak, in which no peak is detected while the component is being held and the peaks attributed to components held for different times, from the mass spectra of the reference sample and the unknown sample.
Preferably, furthermore, the degree of similarlity of the peak of the object component is verified by comparing the half-width of the peak/the peak intensity of the object component in the mass chromatogram of mass number for determination of the reference sample and the unknown sample. This makes it possible to examine the influence caused by the contamination of the apparatus and the deterioration of the column and, hence, to judge the reliability of the results of determination.
Preferably, furthermore, the intensity ratio of the mass numbers is found at which a characteristic peak is obtained in the object component, and is compared with the intensity ratio of an unknown sample. This makes it possible to verify whether the mass number for determination is separated in terms of mass from the adjacent peaks and, hence, to know the influence from the peaks of other components.
Preferably, as a report of reliability, the degree of analogy calculated between the mass spectrum of the reference sample that is automatically purified and the mass spectrum of the unknown sample. This enables the person who conducts the analysis to confirm the reliability of the results of determination in terms of numerical values. By displaying the normalized spectra of the two mass spectra and the differential spectrum between the two mass spectra, furthermore, the person who conducts the analysis can visually confirm the reliability; i.e., the person who conducts the analysis can verify the validity of the results of determination based upon the judgment by both the numerical values and the screen.
On the screen for reporting reliability, preferably, the mass used for the determination and the mass used for a reference are distinctly displayed in different colors or using different symbols or different kinds of line on the mass spectrum of the unknown sample and on the mass spectrum of the reference sample that are automatically purified or on the differential spectrum thereof. Then, the person who conducts the analysis can visually confirm whether the object component is quantitatively separated from the adjacent peaks on the chromatogram, precluding unadequate quantitative mass.
Preferably, the mass spectrum of the reference sample at the time of generating the calibration curve is compared with the mass spectrum for confirming the reliability that has been registered in advance, and the intensity ratio of the mass spectra at the same concentration and the degree of analogy are used as indexes of reliability of the apparatus. This makes it possible to verify the influence of the interface unit, the influence of a drop in the sensitivity due to contamination of the ion source and deterioration in the detector and the influence of a change in the mass spectrum pattern. Therefore, the person who conducts the analysis can easily know the timing of maintenance of the apparatus. If the value is greater than a predetermined value, it is ensured that the apparatus is in a state in which quantitative analysis can be done.